Thermoplastic elastomers having improved low temperature properties

ABSTRACT

Thermoplastic elastomers having improved low temperature properties are provided by incorporating suitable low molecular weight ester plasticizer into blends of crystalline polyolefin homopolymer or copolymer and olefinic rubber. The rubber component of the composition is at least partially cured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to thermoplastic elastomers having improved lowtemperature performance characteristics. A thermoplastic elastomer isgenerally defined as a polymer or blend of polymers that can beprocessed and recycled in the same way as a conventional thermoplasticmaterial, yet has properties and performance similar to that ofvulcanized rubber at service temperatures. Blends or alloys of plasticand elastomeric rubber have become increasingly important in theproduction of high performance thermoplastic elastomers, particularlyfor the replacement of thermoset rubber in various applications.

2. Description of the Related Art

Polymer blends which have a combination of both thermoplastic andelastic properties are generally obtained by combining a thermoplasticpolyolefin with an elastomeric composition in a way such that theelastomer is intimately and uniformly dispersed as a discreteparticulate phase within a continuous phase of the thermoplastic. Earlywork with vulcanized compositions is found in U.S. Pat. No. 3,037,954which discloses static vulcanization as well as the technique of dynamicvulcanization wherein a vulcanizable elastomer is dispersed into aresinous thermoplastic polymer and the elastomer is cured whilecontinuously mixing and shearing the polymer blend. The resultingcomposition is a microgel dispersion of cured elastomer, such as butylrubber, chlorinated butyl rubber, polybutadiene or polyisobutene in anuncured matrix of thermoplastic polymer such as polypropylene. Thispatent describes the use of oil additives derived from coal tar, pinetar or petroleum in the composition.

In U.S. Pat. No. Re. 32,028 polymer blends comprising an olefinthermoplastic resin and an olefin copolymer rubber are described,wherein the rubber is dynamically vulcanized to a state of partial cure.The resulting compositions are reprocessible. The addition of variouslubricants to the cured blend at about one phr is taught to be usefulfor improving extrusion quality of the compositions.

U.S. Pat. Nos. 4,130,534 and 4,130,535 disclose thermoplastic elastomercompositions comprising butyl rubber and polyolefin resin, and olefinrubber and polyolefin resin, respectively. The compositions are preparedby dynamic vulcanization and the rubber component is cured to the extentthat it is essentially insoluble in conventional solvents. The additionof plasticizers and aromatic, naphthenic and paraffinic extender oils tothe blend is suggested. No details are given regarding the choice orsuitability of any particular class or type of plasticizers. It is wellknown that different rubbers are compatible with certain types ofplasticizers and that not all plasticizers are suitable with allrubbers.

In U.S. Pat. No. 5,157,081 a dynamically vulcanized blend is describedcomprising a first butyl rubber based elastomer and a secondethylene-propylene polymer elastomer in a matrix of polyolefinic resin.Rubber process oils derived from petroleum fractions may be included,and a general suggestion is made that organic esters and other syntheticplasticizers can be used.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that a thermoplasticelastomer composition having improved low temperature properties isprovided by incorporating certain types of low molecular weight esterplasticizers into a blend of crystalline polyolefin homopolymer orcopolymer and olefinic rubber. The rubber component of the compositionis usually present as very small, i.e. micro-size, particles in thethermoplastic matrix, and it is preferably at least partially cured.Co-continuous morphologies are also possible. Unexpectedly, theinclusion of these organic esters in the composition provides athermoplastic elastomer which has a significantly lowered glasstransition temperature of both the rubber and polyolefin phases andimproved impact strength at low temperatures, while maintaining thedesirable properties of low compression set, high tear strength and gooddynamic properties over a broad temperature range. The compositions haveutility as constant velocity joint boots, rack and pinion boots,automotive elastoplastic components and mechanical rubber-plastic(thermoplastic elastomer) goods which need to be serviceable at lowtemperatures, e.g. -40° C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Polyolefin

Polyolefins suitable for use in the compositions of the inventioninclude thermoplastic, crystalline polyolefin homopolymers andcopolymers. They are desirably prepared from monoolefin monomers having3 to 6 carbon atoms, such as propylene, 1-butene, isobutylene, 1-penteneand the like, with propylene being preferred. As used in thespecification and claims the term polypropylene includes homopolymers ofpropylene as well as reactor copolymers of polypropylene which cancontain about 1 to about 20 wt % of ethylene or an α-olefin comonomer of4 to 16 carbon atoms, and mixtures thereof. The polypropylene can behighly crystalline isotactic or syndiotactic polypropylene, usuallyhaving a narrow range of glass transition temperature (T_(g)).Commercially available polyolefins may be used in the practice of theinvention.

The amount of polyolefin found to provide useful compositions isgenerally from about 10 to about 90 weight percent, based on the weightof the rubber and polyolefin. Preferably, the polyolefin content willrange from about 60 to about 90 percent by weight.

Olefinic Rubber

Suitable monoolefin copolymer rubbers comprise non-polar, essentiallynon-crystalline, rubbery copolymers of two or more α-monoolefins,preferably copolymerized with at least one polyene, usually a diene.Saturated monoolefin copolymer rubber, for example ethylene-propylenecopolymer rubber (EPM) can be used. However, unsaturated monoolefinrubber such as EPDM rubber is more suitable. EPDM is a terpolymer ofethylene, propylene and a non-conjugated diene. Satisfactorynon-conjugated dienes include 5-ethylidene-2-norbornene (ENB);1,4-hexadiene; 5-methylene-2-norbornene (MNB); 1,6-octadiene;5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene;1,4-cyclohexadiene; dicyclopentadiene (DCPD); and the like.

Butyl rubbers are also useful in the compositions of the invention. Asused in the specification and claims, the term "butyl rubber" includescopolymers of an isoolefin and a conjugated monoolefin, terpolymers ofan isoolefin, a conjugated monoolefin and divinyl aromatic monomers, andthe halogenated derivatives of such copolymers and terpolymers. Theuseful butyl rubber copolymers comprise a major portion of isoolefin anda minor amount, usually less than 30 wt %, of a conjugated multiolefin.The preferred copolymers comprise about 85-99.5 wt % of a C₄₋₇ isoolefinsuch as isobutylene and about 15-0.5 wt % of a multiolefin of 4-14carbon atoms, such as isoprene, butadiene, dimethyl butadiene andpiperylene. Commercial butyl rubber, useful in the invention, is acopolymer of isobutylene and minor amounts of isoprene. Other butyl co-and terpolymer rubbers are illustrated by the description in U.S. Pat.No. 4,916,180, which is fully incorporated herein by this reference.

Another suitable copolymer within the scope of the olefinic rubber ofthe present invention is a copolymer of a C₄₋₇ isomonoolefin and apara-alkylstyrene, and preferably a halogenated derivative thereof. Theamount of halogen in the copolymer, predominantly in thepara-alkylstyrene, is from about 0.1 to about 10 wt %. A preferredexample is the brominated copolymer of isobutylene andpara-methylstyrene. These copolymers are more fully described in U.S.Pat. No. 5,162,445, which is fully incorporated herein by thisreference.

A further olefinic rubber suitable in the invention is natural rubber.The main constituent of natural rubber is the linear polymercis-1,4-polyisoprene. It is normally commercially available in the formof smoked sheets and crepe. Synthetic polyisoprene can also be used.

Blends of any of the above olefinic rubbers can be employed, rather thana single olefinic rubber.

In preparing the compositions of the invention, the amount of olefinicrubber generally ranges from about 90 to about 10 weight percent, basedon the weight of the rubber and polyolefin. Preferably, the olefinicrubber content will be in the range of from about 40 to about 10 weightpercent.

Ester Plasticizer

The addition of certain low to medium molecular weight (<10,000) organicesters and alkyl ether esters to the compositions of the inventiondramatically lowers the T_(g) of the polyolefin and rubber components,and of the overall composition, and improves the low temperatureproperties, particularly flexibility and strength. It is believed thatthese effects are achieved by the partitioning of the ester into boththe polyolefin and rubber components of the compositions. Particularlysuitable esters include monomeric and oligomeric materials having anaverage molecular weight below about 2000, and preferably below about600. It is important that the ester be compatible, or miscible, withboth the polyolefin and rubber components of the compositions, i.e. thatit mix with the other components to form a single phase. The estersfound to be most suitable were either aliphatic mono- or diesters oralternatively oligomeric aliphatic esters or alkyl ether esters.Polymeric aliphatic esters and aromatic esters were found to besignificantly less effective, and phosphate esters were for the mostpart ineffective.

Esters may be screened for suitability by a simple test of their abilityto swell a polyolefin such as polypropylene. For the purposes of thisinvention, polypropylene samples (2.0×20×50 mm) were immersed in variousester plasticizers or non-ester diluents such as mineral oils, and wereswollen at 125° C. to constant weight (normally about 24 hours). If thetotal change in weight was greater than 40%, the diluent was consideredsignificantly compatible with the polypropylene and therefore suitablefor preparing compositions with enhanced low temperature performance.

Examples of esters which have been found satisfactory for use in thepresent invention include isooctyltallate, isooctyloleate,n-butyltallate, n-butyloleate, butoxyethyloleate, dioctylsebacate, di2-ethylhexylsebacate, dioctylazelate, diisooctyldodecanedioate,alkylalkylether diester glutarate and oligomers thereof. Other analoguesexpected to be useful in the present invention include alkyl alkylethermono- and di-adipates, mono- and dialkyl adipates, glutarates,sebacates, azelates, ester derivatives of castor oil or tall oil andoligomeric mono- and diesters or mono- and dialkyl ether esterstherefrom. Isooctyltallate and n-butyltallate are particularlypreferred. These esters may be used alone in the compositions, or asmixtures of different esters, or they may be used in combination withconventional hydrocarbon oil diluents or process oils, e.g. paraffinoil. The amount of ester plasticizer in the composition will generallybe less than about 250 phr, and preferably less than about 175 phr.

Additives

In addition to the polyolefin, rubber and ester components, thecompositions of the invention include curatives and may also includereinforcing and non-reinforcing fillers, antioxidants, stabilizers,rubber processing oil, extender oils, lubricants, antiblocking agents,antistatic agents, waxes, foaming agents, pigments, flame retardants andother processing aids known in the rubber compounding art. Suchadditives can comprise up to about 50 wt % of the total composition.Fillers and extenders which can be utilized include conventionalinorganics such as calcium carbonate, clays, silica, talc, titaniumdioxide, carbon black and the like. The rubber processing oils generallyare paraffinic, naphthenic or aromatic oils derived from petroleumfractions. The type will be that ordinarily used in conjunction with thespecific rubber or rubbers present in the composition, and the quantitybased on the total rubber content may range from zero to a few hundredphr. However, it is an important aspect of the present invention thatprocessing oil need not be present, and in fact it may be totallyreplaced by the ester plasticizer component of the composition. In otherword, depending upon the properties desired in the thermoplasticelastomers of the invention, the composition may be free of processingoil or it may contain a combination of processing oil and ester.

Processing

The olefin rubber component of the thermoplastic elastomer is generallypresent as small, i.e. micro-size, particles within a continuouspolyolefin matrix, although a co-continuous morphology or a phaseinversion is also possible depending on the amount of rubber relative toplastic, and the cure system or degree of cure of the rubber. The rubberis desirably at least partially crosslinked, and preferably iscompletely or fully crosslinked. The partial or complete crosslinkingcan be achieved by adding an appropriate rubber curative to the blend ofpolyolefin and rubber and vulcanizing the rubber to the desired degreeunder conventional vulcanizing conditions. However, it is preferred thatthe rubber be crosslinked by the process of dynamic vulcanization. Asused in the specification and claims, the term "dynamic vulcanization"means a vulcanization or curing process for a rubber contained in athermoplastic elastomer composition, wherein the rubber is vulcanizedunder conditions of high shear at a temperature above the melting pointof the polyolefin component. The rubber is thus simultaneouslycrosslinked and dispersed as fine particles within the polyolefinmatrix, although as noted above other morphologies may also exist.Dynamic vulcanization is effected by mixing the thermoplastic elastomercomponents at elevated temperature in conventional mixing equipment suchas roll mills, Banbury mixers, Brabender mixers, continuous mixers,mixing extruders and the like. The unique characteristic of dynamicallycured compositions is that, notwithstanding the fact that the rubbercomponent is partially or fully cured, the compositions can be processedand reprocessed by conventional plastic processing techniques such asextrusion, injection molding and compression molding. Scrap or flashingcan be salvaged and reprocessed.

Those ordinarily skilled in the art will appreciate the appropriatequantities, types of cure systems and vulcanization conditions requiredto carry out the vulcanization of the rubber. The rubber can bevulcanized using varying amounts of curative, varying temperatures andvarying time of cure in order to obtain the optimum crosslinkingdesired. Any known cure system for the rubber can be used, so long as itis suitable under the vulcanization conditions with the specificolefinic rubber or combination of rubbers being used and with thepolyolefin. These curatives include sulfur, sulfur donors, metal oxides,resin systems, peroxide-based systems and the like, both with andwithout accelerators and co-agents. Such cure systems are well known inthe art and literature of vulcanization of elastomers.

The terms "fully vulcanized" and "completely vulcanized" as used in thespecification and claims means that the rubber component to bevulcanized has been cured to a state in which the elastomeric propertiesof the crosslinked rubber are similar to those of the rubber in itsconventional vulcanized state, apart from the thermoplastic elastomercomposition. The degree of cure can be described in terms of gel contentor, conversely, extractable components. Alternatively the degree of curemay be expressed in terms of crosslink density. All of thesedescriptions are well known in the art, for example in U.S. Pat. Nos.5,100,947 and 5,157,081, both of which are fully incorporated herein bythis reference.

The following general procedure was used in the preparation ofthermoplastic elastomers of the invention as set forth in the examples.The polyolefin and rubber were placed in a heated internal mixer, withan appropriate portion of the ester and other desired additives. Themixture was heated to a temperature sufficient to melt the polyolefincomponent, the mixture was masticated and curative was added whilemastication continued. After a maximum of mixing torque indicated thatvulcanization had occured, additional ester was added as indicated, andmixing was continued until the desired degree of vulcanization wasachieved. The order of addition of the various components may vary. Thecompositions were then removed from the mixer, molded and tested fortheir physical properties.

The invention will be better understood by reference to the followingexamples which serve to illustrate but not limit the present invention.

EXAMPLE 1

After screening diluents with the swelling test described earlier,compositions were prepared to demonstrate the effect of includingcertain organic esters in thermoplastic elastomers, as compared tomineral oils. The rubber, plastic, a phenolic curing agent and additiveswere blended in an electrically heated Brabender mixer of 65-80 cm³capacity, at a mixing speed of 100 rpm and a temperature of 120° to 190°C. Before melting of the polyolefin component, a Lewis acid was added tothe blend and mixing was continued. The mixing temperature as a functionof time was observed, and the onset of vulcanization was accompanied bya rapid increase in mixing torque at around 185° C. Mixing was stoppedwhen the torque became relatively constant. The compositions wereremoved from the mixer and sheets were molded at 190° C. and used formeasurement of physical properties.

The key property for determining the efficacy of a plasticizer inimproving the low temperature behavior of a thermoplastic elastomer isthe glass transition temperature of both the rubber and plasticcomponents. The glass transition temperatures (T_(g)) were measuredusing a Rheometrics RDA II dynamic mechanical spectrometer, using thetorsional mode. The dynamic strain was 0.5%; the autostrain feature wasused; the frequency was 10 Hz.

Control blend "A" contained no ester plasticizer, and had the followingcomposition:

    ______________________________________                                        Ingredient          %      PHR                                                ______________________________________                                        EPDM (Vistalon 8600)                                                                              25.71  100                                                Isotactic Polypropylene                                                                           56.34  219.10                                             Fillers:                                                                      Active black (40%)   4.96  19.28                                              Clay                10.29  40.00                                              Curatives            2.70  10.50                                              ______________________________________                                    

The remaining blends contained ester plasticizer or conventionalprocessing oil, and had the following composition "B":

    ______________________________________                                        Ingredient          %      PHR                                                ______________________________________                                        EPDM (Vistalon 8600)                                                                              19.28  100                                                Isotactic Polypropylene                                                                           42.22  219.10                                             Fillers:                                                                      Active black (40%)   3.72  19.28                                              Clay                 7.71  40.00                                              Curatives            2.03  10.50                                              Oil/Ester plasticizer                                                                             25.05  130                                                ______________________________________                                    

The glass transition temperatures of the compositions are set forth inTable 1. The oils and plasticizers were selected using the swellingscreening test described earlier.

    __________________________________________________________________________    Blend                                                                             Oil/Ester           Rubber T.sub.g °C.                                                               Plastic T.sub.g °C.                  __________________________________________________________________________    A   None                  -41     +10                                         B1  Amoco Rycon ® Grease                                                                            -47      -1                                         B2  Sunpar ® 150M Paraffinic Oil                                                                    -46      -5                                         B3  Parapol ® 750 Polybutene                                                                        -47      -5                                         B4  Cyclolube ® 213 Naphthenic Oil                                                                  -48      -5                                         B5  Cyclolube 4053 Naphthenic Oil                                                                       -50      -5                                         B6  Cyclolube 410 Naphthenic Oil                                                                        -51      -5                                         B7  Amoco 9012 Polypropene                                                                              -45     -10                                         B8  Alkylalkylether diester glutarate                                                                   -55     -11                                             (Plasthall ® 7041)                                                    B9  Diisooctyldodecanedioate (Plasthall D10DD)                                                          -56     -14                                         B10 Dioctylazelate (Plasthall DOZ)                                                                      -60     -22                                         B11 Dioctylsebacate (Plasthall DOS)                                                                     -60     -18                                         B12 Butoxyethyloleate (Plasthall 325)                                                                   -66     -20                                         B13 n-Butyloleate (Plasthall 914)                                                                       -71     -24                                         B14 n-Butyltallate (Plasthall 503)                                                                      -70     -24                                         B15 Isooctyltallate (Plasthall 100)                                                                     -75     -26                                         __________________________________________________________________________

As is apparent from the foregoing, the inclusion of organic alkyl andalkyl ether esters in dynamically vulcanized thermoplastic elastomersubstantially reduces the T_(g) of both the rubber and plasticcomponents, in comparison to the conventional processing oils andgrease.

EXAMPLE 2

Compositions containing high molecular weight (polymeric) esterplasticizers were compared with a composition of the invention todemonstrate that the polymeric materials are not very effective inreducing T_(g). Blends were prepared as in Example 1, using the sameproportions of components as composition "B", except that the amount ofester plasticizer was 70 phr in all cases.

                  TABLE 2                                                         ______________________________________                                                             Avg.      Rubber                                                                              Plastic                                  Blend   Ester Plasticizer                                                                          M.W.      T.sub.g °C.                                                                  T.sub.g °C.                       ______________________________________                                        B16     n-Butyltallate                                                                             <400      -65   -15                                      B17     Polyester adipate                                                                           6000     -41    +5                                              (Paraplex ® G-40)                                                 A       None         --        -41   +10                                      ______________________________________                                    

It is apparent that the polymeric ester did not have the same effect oflowering the T_(g) of both the rubber and plastic components of thethermoplastic elastomer, compared to monomeric esters such asn-butyltallate. This phenomenon is related to the increase incombinatorial entropy of mixing which is large for monomeric esters.This in turn results in a large and negative free energy of mixing whichfavors miscibility in the case of the monomeric esters but not as muchfor the polymeric esters. This example therefore illustrates theimportance of diluent molecular weight and miscibility for maximumeffect of the plasticizer.

EXAMPLE 3

Blends were prepared wherein combinations of low molecular weight esterand paraffin oil were added to a thermoplastic elastomer. Blends wereprepared as in Example 1, based on composition "B" plus the indicatedadditives, and T_(g) was determined.

                                      TABLE 3                                     __________________________________________________________________________    Blend                                                                             Paraffin Oil (phr)                                                                     n-Butyl tallate (phr)                                                                   Rubber T.sub.g °C.                                                             Plastic T.sub.g °C.                     __________________________________________________________________________    A    0        0        -41     +10                                            B18  0       130       -74     -24                                            B19 30       100       -70     -20                                            B20 60       70        -60     -14                                            B21 70       60        -60     -14                                            B22 100      30        -55     -16                                            B2  130       0        -46      -5                                            __________________________________________________________________________

For a fixed amount of total diluent added (plasticizer and/or oil--130phr in this example) the depression of T_(g) in the thermoplasticelastomers can be controlled by combination of the ester plasticizerwith appropriate amounts of rubber process oil. Mixtures of differentesters together with oil may also be used.

EXAMPLE 4

The effect of addition of low molecular weight esters on the impactstrength of thermoplastic elastomers was studied and compared with theeffect of conventional process oil. Blends were prepared as in Example1, using a 1300 cm³ Banbury mixer, based on composition "A", plus theindicated additives (in phr). The notched Izod impact resistance at -40°C. was determined for each composition following the procedure set forthin ASTM D256-84, using specimens cut from compression molded plaques3.17 mm in thickness.

    ______________________________________                                        Blend -     A1     A2     A3   A4   A5   A6   A7                              ______________________________________                                        Carbon black                                                                              0      100    0    0    100  0    0                               (N326)                                                                        Silica (Hisil 233)                                                                        0      0      100  0    0    100  0                               n-Butyltallate                                                                            0      0      0    130  130  130  0                               Paraffinic oil                                                                            130    130    130  0    0    0    0                               (Sunpar 150M)                                                                 isooctyltallate                                                                           0      0      0    0    0    0    100                             Hardness (Shore D)                                                                        38     38     36   37   37   36   35                              Notched Izod                                                                              82     76     93   414  489  424  427                             Impact                                                                        Strength (J/m ± σ)                                                               ±48 ±35 ±52                                                                             ±48                                                                             ±40                                                                             ±32                                                                             ±47                          ______________________________________                                    

It was observed that the inclusion of an alkyl monoester in place ofparaffinic oil resulted in a marked improvement in toughness at -40° C.,by at least a factor of 5. Such compositions are much more ductile thanthose prepared with hydrocarbon process oils, and have enhancedresistance to cracking at low temperatures.

EXAMPLE 5

Compositions were prepared following the procedure of Example 1, whereinthe point of addition of the ester plasticizer was varied. Composition"A" was utilized, and n-butyltallate plasticizer (130 phr) was added asfollows.

Composition "C"--All plasticizer was added before dynamic vulcanizationof the EPDM rubber in the presence of the polypropylene.

Composition "D"--One half (65 phr) of the plasticizer was added to theformulation prior to dynamic vulcanization, and one half was added afterdynamic vulcanization.

Composition "E"--All plasticizer was added after dynamic vulcanization.Both T_(g) and physical properties were determined for the compositions,and are set forth below.

                  TABLE 5                                                         ______________________________________                                                           C     D       E                                            ______________________________________                                        T.sub.g EPDM phase, °C.                                                                     -76     --      -71                                      T.sub.g Polypropylene phase, °C.                                                            -20     --      -25                                      Density, gm/cm.sup.3 (ASTM D297)                                                                   0.952   0.952   0.953                                    Stress @ break, MPa (ASTM D412)                                                                    13.40   13.24   11.64                                    Strain @ break, % (ASTM D412)                                                                      372      316    249                                      Compression set, 22 hr/100° C., %                                                           72      --       66                                      (ASTM D395B)                                                                  Weight change, 24 hr/125° C.,                                                               59      --       51                                      ASTM 3, % (ASTM D471)                                                         ACR viscosity, poise 1389    1286    872                                      ______________________________________                                    

It can be seen from the foregoing that the properties of thethermoplastic elastomer can be varied by changing the point of additionof the ester plasticizer in relation to the curing step.

EXAMPLE 6

Thermoplastic elastomers based on butyl rubber and polypropylene wereprepared following the technique of Example 1, using two different esterplasticizers, a conventional rubber process oil and a blend of ester andprocess oil. About 90% of the diluents were added before the cure ineach case. Formulations (in phr) and physical properties are set forthin Table 6.

In addition to reduced T_(g) and improved low temperaturecharacteristics, it should be noted that the compositions of theinvention have improved (lowered) damping characteristics, as measuredby Tan delta at 23° C. In contrast, the use of paraffinic oil increasedthe loss tangent at 23° C.

                                      TABLE 6                                     __________________________________________________________________________    Composition     F    G    H    I    J                                         __________________________________________________________________________    Butyl rubber    100  100  100  100  100                                       (Polysar ® Butyl 301)                                                     Polypropylene   20   20   20   20   20                                        (Aristech FP200F)                                                             Polypropylene   180  180  180  180  180                                       (Rexene 51SO7A)                                                               Isooctyltallate 100   0   50    0    0                                        (Plasthall P100)                                                              n-Butyltallate   0    0    0   100   0                                        (Plasthall P503)                                                              Paraffinic oil   0   100  50    0    0                                        (Sunpar 150M)                                                                 Cure system.sup.1                                                                             11   11   11   11   11                                        Stearic acid     1    1    1    1    1                                        Active carbon black 40%                                                                       20   20   20   20   20                                        T.sub.g Butyl rubber phase, °C.                                                        -76  -52  -57  -75  -56                                       T.sub.g Polypropylene, °C.                                                             -22   0   -16  -25  +10                                       Tan Delta @ 23° C.                                                                     0.0537                                                                             0.0800                                                                             0.0581                                                                             0.0386                                                                             0.0638                                    Hardness (Shore D).sup.2                                                                      36   37   35   34   51                                        Stress @ break, MPa                                                                           10.0 12.1 11.4 9.6  16.6                                      Strain @ break, %.sup.3                                                                       246  308  282  258  593                                       Tear strength, kJ/sq m.sup.4                                                                  54   66   60   54   --                                        Compression set (22 hr/100° C.)                                                        72   60   61   79   78                                        Weight change, %                                                                              62   46   51   58   91                                        (ASTM 3, 24 hr/125° C.)                                                __________________________________________________________________________     .sup.1 Phenolic resin (5 phr), SnCl.sub.2 (1 phr), Zinc oxide (5 phr)         .sup.2 ASTM D2240                                                             .sup.3 ASTM D412                                                              .sup.4 ASTM D624                                                         

EXAMPLE 7

The effect of ester concentration levels on the T_(g) and physicalproperties of an EPDM rubber-polypropylene thermoplastic elastomer wasstudied. Composition "A" was utilized, and the technique of Example 1was followed. The concentration of n-butyltallate in the formulation wasvaried from 0 to 219 phr, and the results are set forth in Table 7.

                                      TABLE 7                                     __________________________________________________________________________    Composition  A   A8  A9  A10 A11 A12 A13                                      __________________________________________________________________________    n-Butyltallate (phr)                                                                         0 15  30  70  100 130 219                                      T.sub.g Rubber phase, °C.                                                           -41 -50 -55 -65 -70 -74 -75                                      T.sub.g Polypropylene, °C.                                                          +10 +4.6                                                                              -4.8                                                                              -16 -15 -24 -25                                      Hardness (Shore D)                                                                          58 50  49  42  38  37  27                                       100% Modulus, MPa                                                                          16.2                                                                              16.2                                                                              15.0                                                                              11.7                                                                              15.5                                                                              11.6                                                                              6.5                                      Stress @ break, MPa                                                                        22.3                                                                              22.9                                                                              17.7                                                                              18.5                                                                              21.1                                                                              14.3                                                                              6.6                                      Strain @ break, %                                                                           467                                                                              442 334 493 452 345 110                                      Weight gain, %                                                                              61 58  55  55  47  45  27                                       (24 hr/125° C., ASTM 3)                                                Compression set, %                                                                         --  62  63  64  66  63  59                                       (22 hr/100° C.)                                                        __________________________________________________________________________

It can be seen that the lowering of T_(g) is effective across most ofthe range of ester plasticizer added to the formulations.

EXAMPLE 8

Soft (low modulus) thermoplastic elastomer compositions containingnatural rubber or EPDM rubber or oil-extended EPDM rubber were preparedfollowing the technique described in Example 1, mixed in a 20 literBanbury-type mixer. The effects of ester plasticizer on T_(g), frictioncoefficient and physical properties were determined. The results are setforth in Table 8A. The concentrations of ingredients are expressed asphr.

                                      TABLE 8                                     __________________________________________________________________________    Composition                                                                              K   L   M   N   O   P   Q                                          __________________________________________________________________________    Oil-extended EPDM.sup.1                                                                  200 200 0   0   0   0   0                                          Natural rubber.sup.2                                                                     0   0   0   0   100 100 100                                        EPDM rubber.sup.3                                                                        0   0   100 100 0   0   0                                          Clay       43.46                                                                             43.46                                                                             43.46                                                                             43.46                                                                             0   0   0                                          Mineral filler                                                                           0   0   0   0   50  50  50                                         Zinc Oxide 1.98                                                                              1.98                                                                              1.98                                                                              1.98                                                                              5   5   5                                          Stearic acid                                                                             0   0   0   0   1   1   1                                          Polypropylene A.sup.4                                                                    24  24  40  40  0   0   0                                          Polypropylene B.sup.5                                                                    7   7   7   7   0   0   0                                          Polypropylene C.sup.6                                                                    0   0   0   0   46.8                                                                              46.8                                                                              46.8                                       Paraffinic oil.sup.7                                                                     50  0   0   0   97.5                                                                              0   0                                          Isooctyltallate                                                                          0   50  150 0   0   97.5                                                                              0                                          Color concentrate.sup.8                                                                  3.25                                                                              3.25                                                                              3.25                                                                              3.25                                                                               3.25                                                                              3.25                                                                              3.25                                      Curative A.sup.9                                                                         4   4   4   4   0   0   0                                          Curative B.sup.10                                                                        0   0   0   0   11.7                                                                              11.7                                                                              11.7                                       SnCl.sub.2 1.68                                                                              1.68                                                                              1.68                                                                              1.68                                                                              0   0   0                                          Antioxidant.sup.11                                                                       0   0   0   0   1   1   1                                          __________________________________________________________________________     .sup.1 Epsyn P597 rubber, wxtended with 100 parts paraffin oil (Copolymer     Rubber & Chemical Co.)                                                        .sup.2 CV60 natural rubber, Mooney 60 (Golden Hope Plantations)               .sup.3 Vistalon ® 8600 (Exxon Chemical Co.)                               .sup.4 Rexene ® polypropylene (Rexene Corp.)                              .sup.5 Aristech FP200F (Aristech Corp.)                                       .sup.6 Aristech D008M (Aristech Corp.)                                        .sup.7 Sunpar 150 (Sun Chemical)                                              .sup.8 Americhem 21065 R1                                                     .sup.9 SP-1045 (Schenectady International Inc.)                               .sup.10 HRJ 10518 (Schenectady International Inc.)                            .sup.11 Irganox ® 1010 (General Electric Co.)                        

                                      TABLE 8A                                    __________________________________________________________________________    Composition   K   L   M   N   O   P   Q                                       __________________________________________________________________________    T.sub.g Rubber phase, °C.                                                            -50 -60 -76 -35 -55 -77 -51                                     Hardness (Shore A)                                                                          54   53  53  85  67  64  85                                     Stress @ 100% strain, MPa                                                                   1.8 1.7 1.5 5.9 2.7 2.5 4.5                                     Stress @ break, MPa                                                                         4.89                                                                              4.17                                                                              1.90                                                                              7.33                                                                              4.86                                                                              4.50                                                                              4.46                                    Strain @ break, %                                                                           347 347  270                                                                              184 257 219 178                                     Weight gain, %                                                                              87  109 --  204 123 121 200                                     (24 hr/125° C., ASTM 3)                                                Friction coefficient                                                          against polypropylene                                                         Static        1.80                                                                              1.54                                                                              1.07                                                                              1.53                                                                              1.00                                                                              1.13                                                                              1.40                                    Kinetic       1.62                                                                              1.66                                                                              1.19                                                                              1.55                                                                              1.08                                                                              1.33                                                                              1.22                                    __________________________________________________________________________

As apparent from Example 8, the thermoplastic elastomers of the presentinvention have significantly reduced T_(g) while retaining good physicalproperties.

While the best mode and preferred embodiment of the invention have beenset forth in accord with the Patent Statutes, the scope of the inventionis not limited thereto, but rather is defined by the attached claims.

What is claimed is:
 1. A composition comprising(a) from about 10 toabout 90 wt % thermoplastic, crystalline polyolefin homopolymer orcopolymer, (b) from about 90 to about 10 wt % olefinic rubber, and (c)from about 1 to about 250 parts per hundred parts of rubber of a lowmolecular weight ester plasticizer which is compatible with both thepolyolefin and rubber, wherein said rubber is at least partiallycrosslinked.
 2. The composition of claim 1 wherein the polyolefin is apolymer of a C₂₋₆ monomer or comonomers thereof.
 3. The composition ofclaim 1 wherein the polyolefin is selected from the group consisting ofpolypropylene, poly 1-butene, poly 1-pentene, poly(3-methyl 1-butene),poly(4-methyl 1-pentene) and mixtures thereof.
 4. The composition ofclaim 1 wherein the polyolefin is polypropylene.
 5. The composition ofclaim 1 wherein the rubber is selected from the group consisting of EPDMrubber, EPM rubber, butyl rubber, halogenated butyl rubber, copolymersof isomonoolefin and para-alkylstyrene, natural rubber, polyisoprene andmixtures thereof.
 6. The composition of claim 1 wherein the rubber isEPDM terpolymer rubber.
 7. The composition of claim 1 wherein the esterplasticizer has a molecular weight of about 2000 or less.
 8. Thecomposition of claim 1 wherein the plasticizer is selected from thegroup consisting of monomeric alkyl mono- and diesters, oligomeric alkylmono- and diesters, monomeric alkylether mono- and diesters, andoligomeric alkylether mono- and diesters.
 9. The composition of claim 1wherein the ester plasticizer is selected from the group consisting ofdiisooctyldodecanedioate, dioctylsebacate, butoxyethyloleate,n-butyloleate, n-butyltallate, isooctyloleate, isooctyltallate,dialkylazelate and mixtures thereof.
 10. The composition of claim 1wherein the ester plasticizer is isooctyltallate.
 11. The composition ofclaim 1 wherein the ester plasticizer is n-butyl tallate.
 12. Thecomposition of claim 1 which additionally includes rubber curatives,rubber processing oil, fillers, antioxidants or other additives.
 13. Thecomposition of claim 1 wherein the rubber is fully crosslinked.
 14. Acomposition comprising(a) from about 10 to about 90 wt % ofpolypropylene, (b) from about 90 to about 10 wt % of EPDM terpolymerrubber, based on the total weight of components (a) and (b), and (c)from about 15 to about 65 wt % of isooctyltallate, based on the totalweight of components (a), (b) and (c), wherein said rubber is at leastpartially crosslinked.
 15. The composition of claim 14 wherein therubber is fully crosslinked.